Practical Microwave Applications Research Articles

Ultra-compact half-mode substrate integrated waveguide bandpass filters with IRCSRR metamaterial on reinforced hydrocarbon polymer ceramic composites

In this work, metamaterial-enabled ultra-compact evanescent-mode half-mode substrate integrated waveguide (HMSIW) bandpass filters are developed by loading inner-rotary complementary split-ring resonator (IRCSRR) on reinforced hydrocarbon polymer ceramic composites substrate. In the proposed IRCSRR, inner-rotary slots are etched inside the conventional complementary split-ring resonator (CSRR) metamaterials to enhance the product of equivalent inductance and capacitance without occupying extra circuit area. Therefore, the proposed HMSIW-IRCSRR filters can obtain more size reduction with the same operation frequency as compared with the conventional CSRR-based ones. Similar as the conventional CSRR case, the evanescent-mode transmission below the dominant cutoff frequency of HMSIW can be produced by the negative permittivity effect of IRCSRR, and a transmission zero (TZ) at the upper stopband can be simultaneously generated by the mutual coupling between HMSIW and IRCSRR. Then, to improve the upper stopband performance, source-load coupling topology is utilized in the two-pole filters, which can produce multiple extra TZs. Meanwhile, multiple microstrip L/T-shaped open stubs are employed to introduce hybrid low-pass effect to further extend the upper stopband much wider. To demonstrate the availability of the aforementioned concepts, a series of HSMIW-IRCSRR filters are experimentally designed, fabricated and verified. Measured results shows that both ultra-compact sizes and excellent frequency-selecting performance are achieved simultaneously, as well as good agreement with simulations, all of which illustrating quite good promises for the practical radio frequency and microwave applications.

A Gap Coupled Hexagonal Split Ring Resonator Based Metamaterial for S-Band and X-Band Microwave Applications

A gap coupled hexagonal split ring resonator (GCHSRR) based metamaterial is presented in this paper for S-band and X-band microwave applications with absorptance. This gap coupled hexagonal split ring resonator is the amendment of the typical split-ring resonator (SRR). Three interconnected hexagonal split ring resonators are applied with a stripline to increase the electrical length and coupling effect of the GCHSRR. SRR has an impact on the extraction of effective parameters such as permittivity, permeability and refractive index. The dimension of the proposed GCHSRR unit cell is $10\times 10$ mm 2, which is printed on low-cost FR4 material. The transmission frequency of the proposed GCHSRR unit cell ranges from 3.42 GHz to 3.73 GHz and 11.27 GHz to 11.91 GHz, which makes the metamaterial applicable for S-band and X-band microwave applications. The GCHSRR unit cell has a double negative regime of 7.92 GHz to 9.78 GHz with an effective negative refractive index regime of 6.30 GHz to 10.22 GHz and 11.97 GHz to 12.61 GHz. The effective medium ratio is 8.4, which implies the novelty of the proposed design. Moreover, the GCHSRR has high absorption peaks of 99%, 98%, and 81% at 4.27 GHz, 5.42 GHz, and 12.40 GHz, respectively. An $18\times 20$ GCHSRR array structure is also designed and studied. The effective parameters and the effective medium ratio with a high absorptance make the proposed GCHSRR based metamaterial suitable for practical microwave applications.

A Thin Double-Mesh Metamaterial Radome for Wide-Angle and Broadband Applications at Millimeter-Wave Frequencies

Antireflection has been a critical part in the design of optical and opto-electronic instruments. In the emerging millimeter (mm)-wave technology for the next-generation communication and autonomous driving, antireflection treatment is increasingly important due to the quasi-optical nature of electromagnetic waves at high frequencies. Enclosures that protect radar or communication phased arrays will introduce reflections if they are not designed properly. In this article, a novel metamaterial radome (meta-radome) is developed based on closely spaced metallic square meshes patterned on a thin dielectric substrate. We show that by deliberately employing the coupling between the meshes, the entire structure can be treated as a homogenized metamaterial slab with its wave impedance matched to that of free space. The resulting meta-radome can be optimized to have good transmission (> 90%) over an extremely wide range of angles of incidence (0° – 80°) for both transverse-electric (TE) and transverse-magnetic (TM) polarizations. Since the meta-radome is not resonant, it has a very small Ohmic loss and broad bandwidth. In addition, the proposed meta-radome is very easy to fabricate with standard fabrication techniques. Thus, it can be very attractive for many practical microwave and mm-wave applications.

Extremely Coherent Microwave Emission from Spin Torque Oscillator Stabilized by Phase Locked Loop.

Spin torque oscillator (STO) has been attracting a great deal of attention as a candidate for the next generation microwave signal sources for various modern electronics systems since its advent. However, the phase noise of STOs under free running oscillation is still too large to be used in practical microwave applications, thus an industrially viable means to stabilize its oscillation has been strongly sought. Here we demonstrate implementation of a phase locked loop using a STO as a voltage controlled oscillator (VCO) that generates a 7.344 GHz microwave signal stabilized by a 153 MHz reference signal. Spectrum measurement showed successful phase locking of the microwave signal to the reference signal, characterized by an extremely narrow oscillation peak with a linewidth of less than the measurement limit of 1 Hz. This demonstration should be a major breakthrough toward various practical applications of STOs.

Effect of Bi4B2O9 addition on the sintering temperature and microwave dielectric properties of BaO–Nd2O3–4TiO2 ceramics

The effects of Bi4B2O9 addition on the sintering temperature, phase transition and microwave dielectric properties of BaO–Nd2O3–4TiO2(BNT) ceramics have been investigated. With 10 wt% Bi4B2O9 addition, the sintering temperature of the BNT ceramics can be lowered down to about 1,150 °C. The secondary phase was observed at the level of 15 wt% Bi4B2O9 addition. The Bi4B2O9 addition can significantly affects the microwave dielectric properties. The Q × f0 value is a function of the sintering temperature and the Bi4B2O9 content. For the samples sintered at 1,150 °C, Q × f0 value varies from 6,300 to 3,300 GHz as the Bi4B2O9 addition increases from 5 to 20 wt%. The addition of Bi4B2O9 does not induce much degradation in er but modified the τf value to near zero. Typically, When 10 wt% Bi4B2O9 is added, the τf of the ceramics could be tuned to a near-zero value (~1.2 ppm/°C), a substantial er (~86) and Q × f0 (~4,670 GHz) could also be achieved simultaneously. The Bi4B2O9 is an efficient sintering additive to decrease the sintering temperature and tune the τf value of the microwave dielectric materials for the practical microwave applications.

Photonic Microwave Applications of the Dynamics of Semiconductor Lasers

In this paper, major photonic microwave generation and modulation methods are described. Their advantages and limitations are identified and compared through the analysis of the key characteristics relevant to practical photonic microwave applications. The focus of this paper is on the photonic microwave based on the nonlinear dynamics of optically injected semiconductor lasers. Both single-beam optically injected semiconductor lasers and dual-beam optically injected semiconductor lasers are considered. In particular, the three dynamic states of stable injection locking, period-one oscillation, and period-two oscillation are considered and demonstrated for photonic microwave generation, modulation, and conversion applications. Several prospects for future research and development in this area are discussed.

TUNABLE MICROSTRIP FILTERS USING SELECTIVELY ETCHED FERROELECTRIC THIN-FILM VARACTORS FOR COUPLING

ABSTRACT We report on the use of patterned ferroelectric films to fabricate proof of concept tunable one-pole microstrip filters with excellent transmission and mismatch/reflection properties at frequencies up to 24 GHz. By controlling the electric field distribution within the coupling region between the resonator and input/output lines, sufficiently high loaded and unloaded Q values are maintained so as to be useful for microstrip filter design, with low mismatch loss. In the 23–24 GHz region, the filter was tunable over a 100 MHz range, the loaded and unloaded Q values were 29 and 68, respectively, and the reflection losses were below −16 dB, which demonstrates the suitability of these films for practical microwave applications.

BaxSr1−xTiO3Thin Film Ferroelectric-Coupled Microstripline Phase Shifters with Reduced Device Hysteresis

In this work, we present experimental results on the performance of coupled microstripline phase shifters (CMPS) fabricated using BaxSr1−xTiO3 (BST) ferroelectric thin films. The CMPS were fabricated using commercially available pulsed laser deposition BST films with Ba:Sr ratios of 30:70 and 20:80. Microwave characterization of these CMPS was performed at upper Ku-band frequencies, particularly at frequencies near 16 and 18 GHz. The quality of performance of the CMPS was studied based on their relative phase shift (Δϕ=ϕnV−ϕ0V, where n=0–400 V DC) and insertion loss within the DC bias range of 0–400 V (i.e., E-field ranges within 0–53 V/μm). The performance of the CMPS was tested as a function of temperature to investigate their operation in the paraelectric as well as in the ferroelectric state (i.e., above and below the Curie temperature, respectively). It was observed that for the CMPS fabricated with the BST films, with Ba:Sr ratio of 30:70, the performance was very good with Δϕ up to 400° and nominal insertion losses of ∼3 dB. In addition, these devices were hysteresis-free in the paraelectric state and only showed Δϕ hysteresis while performing in the ferroelectric state. In contrast, while the CMPS made with Ba:Sr ratios of 20:80 exhibited very good values of Δϕ, they exhibited a mild hysteresis both in the paraelectric and ferroelectric states. X-ray diffraction studies indicate that the 30:70 films exhibit almost a 1:1 ratio between the in-plane and out-of-plane lattice parameters, suggesting that their cubic structure creates strain-free films conducive to CMPS devices with reduced hysteresis in the paraelectric state. Elimination of Δϕ hysteresis is essential because many practical microwave applications such as voltage-controlled oscillators and beam steerable devices, particularly electronically steerable phased array antennas, rely on accurate phase shift versus tuning voltage profiles required for reliable device operation. Accordingly, the optimization of the interplay between film microstructure, Ba content, and dielectric constant is critical for reliable CMPS devices.

LTCC broadband deep embedded interconnects (DEI) with application for embedded bandpass filter

AbstractCareful design of via transitions intended for use in practical microwave applications is needed to realize the advantages of low‐temperature co‐fired ceramic (LTCC), such as highly integrated buried passive circuits. Grounded coplanar waveguide (GCPW) to asymmetrical stripline vertical interconnects is optimized for thick LTCC substrate. The focus is to develop a vertical transition through thick substrate supporting deep embedded interconnects (DEI). The measured results demonstrate vertical transitions with good performance up to 20 GHz. Embedded LTCC bandpass filter with such vertical transition has been demonstrated with an insertion loss of 2.2 dB and return loss better than −20 dB at 16.2 GHz. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 179–181, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11007

Microwave propagation characteristics of a high-temperature superconducting variable spacing parallel plate transmission line

A sinusoidal field solution for a high-temperature superconducting variable spacing parallel plate transmission line is derived. This solution demonstrates how to relate the propagation characteristics to the thicknesses and material parameters of the variable spacer and superconducting films in addition to the dielectric substrates. Then, a numerical analysis of the attenuation constant and phase velocity as a function of the dielectric spacer thickness is made. In addition, some further numerical results from this solution show that the roles played by the thicknesses of the two dielectric substrates are insignificant and can be neglected in practical microwave applications.

High performance microwave power GaN/AlGaN MODFETs grown by RF-assisted MBE

High performance GaN/AlGaN MODFETs grown by MBE directly on SiC substrate have been successfully fabricated and characterised. The epitaxial layers of the device were grown by RF-assisted MBE. Excellent device uniformity, reproducibility and scalability were obtained. Maximum output density of 6.5 W/mm was obtained for a 0.1 mm device. On scaling to 1.0 mm gate-width, a total output power of 6.3 W with 38% PAE at 10 GHz was achieved. These device results demonstrate the excellent potential of GaN-based FETs as power cells for practical microwave applications.

Device characteristics of scaled GaN/AlGaN MODFETs

GaN/AlGaN MODFETs with gate-widths varying from 0.2 to 1 mm have been successfully fabricated, and the device characteristics have been systematically investigated. The epitaxial layers were grown directly on sapphire substrates by RF-assisted MBE. Thick-airbridge technology was employed in the fabrication of large gate periphery devices. Very stable and reproducible device characteristics have been obtained for devices with a total gate width of up to 1 mm. These device results demonstrated the excellent potential of GaN-based FETs as power cells for practical microwave applications.

The Excitation and Detection of Surface-Generated Bulk Waves

Absrruct-The performance of a conventional pair of surface acoustic wave interdigital transducers (IDT’s) used to generate bulk acoustic waves is analyzed. An IDT located on the upper surface of a thick, rotated Ycut quartz crystal acts as the acoustic equivalent of an array antenna, launchingacollimated beam into the crystal bulk. The beam is reflected off the crystal bottom and redirected towards the upper crystal surface where it is intercepted by a second receiving IDT. Closed-form expressions are derived for the important electrical and acoustical delay line characteristics and comparison is made with experimental measurements. The analyzed characteristics of the reflected bulk wave (RBW) delay line are significantly different from either the SAW or SSBWand include a) a frequency bandwidth directly proportional to transducer length, b) a center frequency determined not by finger-to-finger spacing but rather by the ratio of transducer separation to crystal thickness, c) a nonresonant radiation resistance, d) the capability to synthesize filter designs in which the frequency response is proportional to the correlation of the individual transducer finger weightings, and e) the capability to modify temperature stability by change of transducer separation and crystal thickness. ULK ACOUSTIC wave radiation generated by interdigital B transducers has historically been considered as spurious, often degrading or interfering with the performance of devices based upon surface acoustic wave (SAW) excitation. Within the last several years, however, there has been increased interest in utilizing the bulk waves generated by IDT’s for practical microwave applications. Such surface-generated bulk waves make use of the IDT as an acoustic equivalent of a phasedarray antenna, with the electrode fingers constituting the array elements. The phasing between these elements is controlled by the applied signal frequency thereby allowing the direction of the acoustic beam radiated into the bulk to be scanned.

Dielectric waveguides and waveguide devices for microwave applications†

A survey of the state of the art in Dieleetric Waveguides (DW), stressing in particular the practical microwave applications, is given. The principles for designing DW, fixing and joining devices, launchers, various multiport networks, etc. are presented. A simple theory to calculate parameters of multiport networks with distributed coupling is developed. Some microwave problems which it is reasonable to solve making use of DW are discussed. Advice on the frequency range and materials applied is given.

Microwave surface resistance of a superconducting Mo-Re alloy

By using a Mo 0.75 Re 0.25 alloy endplate on a Nb microwave cavity (TE 011 mode, resonant at 11.2 GHZ), an upper bound for the residual surface resistance of this alloy was shown to be 2.8 µ-ohm, a lower bound for the breakdown field was shown to be 102 G. In view of the fact that these properties were determined at 11.2 GHZ on the first Mo-Re endplate made with no particular effort devoted to optimization of surface quality, this material is deserving of further consideration for practical microwave applications.

Ferrite-Tunable Microwave Cavities and the Introduction of a New Reflectionless, Tunable Microwave Filter

Large ferrite samples are placed in microwave cavities with the object of achieving tunable microwave cavities. Experimental data, at X band frequencies, on ferrite tuning of conventional band-pass and band elimination cavities are presented. Curves of applied dc magnetic field vs cavity resonant frequency, bandwidth, loss, cavity Q, and window coupling coefficients are included. Of particular interest are the results obtained with a new type cavity filter. With a single circularly polarized cavity, a reflectionless filter is achieved which couples nearly 100 per cent of the energy from the main waveguide at the cavity resonant frequency. Experimental results, on the ferrite loading of these circularly polarized cavities, are presented, and a number of practical microwave applications are discussed.